This proposal is to study a novel protein disulfide-thiol interchange activity associated with the outer plasma membrane leaflet at the surface of cancer cells (designated tTIP) and its counterpart in nontransformed cells (designated CTIP). The activity is unusual in that it is responsive to a small group of drugs representing potential quinone site inhibitors such as antitumor sulfonylureas and a vanilloid, capsaicin. The tTIP protein has been purified to near homogeneity from HeLa and from sera of cancer patients and consists of a complex of at least two (possibly three or more) peptide chains that, through strong hydrophobic interactions, form relatively stable multimers. Monoclonal antisera produced to a circulating form of tTIP from sera of cancer patients crossreact with the cell surface form and prevent growth of and induce apoptosis in HeLa cells growing in culture. Based on the monoclonal antisera results and results with inhibitory drugs targeted to tTIP, the function of the protein would appear to reside somewhere in the growth cycle, possibly to facilitate unregulated cell enlargement. This project is to complete the molecular characterization of tTIP, including subunit identification and molecular cloning. Additionally, work will be initiated to identify and characterize the proteins responsible for the corresponding CTIP activities of non-transformed cells. The experimental systems will utilize primarily cells of human origin in culture (HeLa and WI-38) and plasma membranes and TIP proteins isolated from cultured cells.